Current legislation requires the use of contained piping systems when transporting contaminants underground. This legislation is particularly applicable to the fuel-handling market. Fuel, e.g., gasoline, is stored underground in tanks and is then piped to overground fuel pumps. To prevent contamination of the surrounding ground, the legislation requires that a secondary pipe, also referred to as merely a "secondary," is used to encase the main pipe and contain any leakage from the main pipe, also referred to as the "primary." As a result, since the tank is a low point in the system, any leakage contained in the second pipe flows, due to gravity, back to the tank. Such systems are sometimes referred to as dual containment systems.
This legislation has given rise to the need for a secondary piping system which is easy to install and economical. A substantial portion of the cost of these systems is driven by the technique used to join the secondary pipes forming the containment system.
In an assembly of contained piping, it is desired, and often required, that the primary connection be visible during an initial pressure test of the system to insure integrity at test pressures. Typically, the secondary is designed with a gap over the points where the primary is joined to allow inspection of the joint under test pressures. Closure of this gap can become difficult depending on the intended service and system design. Usually this gap is closed with a two-piece fitting ("clam-shell" design) such as by manufacturing the secondary fitting element in two length-wise elements, i.e., split longitudinally into equal halves. However, the junction between the two halves create a low strength point which usually will not perform to the level of the rest of the system. Even though the secondaries are usually rated for low pressures, there are occasions in which the secondary is required to be rated at the same pressure as the primary. The joining methods to resist pressures at primary ratings are costly.
It is therefore desirable to provide a cost effective and high strength technique for closing the secondary at the joints which is capable of operating under the same pressures as the primary.